Processes for the preparation of stable, aqueous polyurethane polyurea dispersions are known (e.g. DBP No. 1,184,946 which is equivalent to U.S. Pat. No. 3,388,087; DAS No. 1,237,306 which is equivalent to U.S. Pat. No. 3,461,103; DOS No. 1,495,745 which is equivalent to U.S. Pat. No. 3,479,310 and German DOS 1,770,068 which is equivalent to U.S. Pat. No. 3,756,992 as well as German DOS 2,019,324 which is equivalent to U.S. Pat. No. 3,686,108 and German Pat. No. 1,178,586 which is equivalent to British Pat. No. 1,043,260 and also DOS No. 1,595,602; see also D. Dieterich et al, Angew. Chem. 82, 53 (1970)). The dispersions already described are based on the principle of incorporating hydrophilic centers into a macromolecular chain of a polyurethane polyurea molecule. In the known dispersions, these hydrophilic centers or so-called "internal emulsifiers" are ionic groups or ether functions. The ionic groups are either incorporated in the prepolymer in the form of certain diols or used as modified amines for chain lengthening the prepolymers, each of which has at least two NCO end-groups.
High quality polyurethane films which are suitable, e.g. for coating textiles, have hitherto been obtained from dispersions produced by processes in which organic solvents were used in the polyaddition reaction. By this method it is possible to operate in homogeneous solutions for obtaining products up to relatively high molecular weights and thus achieve problem-free dispersion. In particular, high quality, finely-divided and stable dispersions may be obtained in this way even with a low ionic group content.
This highly developed process which includes both anionic, cationic and non-ionic emulsifier segments has the disadvantage of requiring extensive operations for distilling off and rectifying the organic solvent. This is connected with a poor volume/time yield in the production process. The organic solvent used as reaction medium increases the risk of explosion and fire during the process. If attempts are made to produce such products without organic solvents one obtains, at best, relatively coarse dispersions the film forming capacity and mechanical properties of which are inadequate for numerous purposes.
A process for solvent-free preparation of polyurethane dispersions is also known, the so-called "melt dispersion process" (DOS No. 1,770,068 which is equivalent to U.S. Pat. No. 3,756,992, D. Dieterich and H. Reiff, Angew. makromol. Chem. 76, 85 (1972)). In this process, an oligourethane which has been modified with ionic groups and contains acylated amino end-groups is reacted with formaldehyde to convert it into the corresponding oligourethane which contains methylol end-groups attached to acylated amino groups and this oligourethane is then chain lengthened by a heat treatment which gives rise to condensation of the reactive methylol end-groups. This chain lengthening reaction may be carried out in the presence of water so that an aqueous dispersion of polyurethane is obtained directly. This process is particularly suitable for producing cationically modified polyurethanes or anionic polyurethanes which contain carboxylate groups. The necessary combination of the isocyanate polyaddition reaction with the above-mentioned chain lengthening reaction by means of polycondensable methylol groups which are attached to acylamino end-groups is somewhat more complicated than the known isocyanate polyaddition carried out by the prepolymer process in which prepolymers which contain isocyanate groups are reacted with conventional chain lengthening agents, such as water or diamines. This extra expenditure could be justified in the process according to DOS No. 1,770,068 on the grounds that this process made it possible for the first time to produce polyurethane dispersions without the aid of special stirrers and without emulsifiers or solvents.
The problem of producing aqueous dispersions of polyurethanes which contain sulphonate groups and are therefore substantially unaffected by electrolytes by a simple process which does not make use of the above aids and is confined to the methods of the isocyanate polyaddition reaction remained unsolved. Qualitatively high grade dispersions of polyurethanes which contain sulphonate groups have hitherto been obtained from prepolymers which contain NCO end-groups by chain lengthening solutions of these prepolymers in organic solvents with diaminosulphonate solutions. Attempts to carry out this process without solvents have hitherto failed; it was impossible to obtain dispersions from which films with acceptable physical properties could be obtained.
It has now surprisingly been found that high quality dispersions of sulphonate group-containing polyurethanes which are substantially free from the influence of electrolytes may be obtained by a simple isocyanate polyaddition reaction without the aid of stirrers with high shearing forces and without the aid of emulsifiers or solvents if quite specific sulphonate group containing diols which will be described below are used in the production of the polyurethanes.